Cita APA (7th ed.)
Spencer, F. D. (1986). Coal Geology and coal, oil, and gas resources of the Erie and Frederick quadrangles, Boulder and Weld Counties, Colorado. United States Government Print. Office.
Cita Chicago (17th ed.)
Spencer, Frank D. Coal Geology and Coal, Oil, and Gas Resources of the Erie and Frederick Quadrangles, Boulder and Weld Counties, Colorado. Washington: United States Government Print. Office, 1986.
Cita MLA (9th ed.)
Spencer, Frank D. Coal Geology and Coal, Oil, and Gas Resources of the Erie and Frederick Quadrangles, Boulder and Weld Counties, Colorado. United States Government Print. Office, 1986.
Atenció: Aquestes cites poden no estar 100% correctes.